Superoxide radicals (02-) are thought to have both beneficial and deleterious effects upon the living cell. Although the 01- radical dismutates spontaneously by a pH dependent mechanisms to 02 and H202, this process is accelerated to near diffusion controlled rates by superoxide dismutases. In the presence of catalytic amounts of metal complexes, however, 02- can initiate the formation of such oxidants as OH. (Fenton reaction), metal-oxy complexes, higher oxidation state metals (Fe-02+, Mn3+ etc.), organic oxy/peroxy radicals, hydroperoxides etc. Under such conditions, the number and oxidative power of such species has increased to a degree where the protective mechanisms in living cells are no longer effective. This may lead to cell disfunction from membrane damage by lipid peroxidation, DNA strand breakage, NADPH/NADH depletion etc. Evidence is accumulating that links such events to paraquat, halogen and anti-cancer drug toxicity, arthritis, tissue damage following reperfusion, dementia etc. The thrust of research described in this proposal for the next three years involves two basic areas: 1) The development of methods to generate metal-oxy complexes and hypervalent metal ions (e.g. Fe(IV)/Fe(V) in isolation in order to study their reactivity with biologically significant compounds; e.g. antioxidants, PUFA's, nucleic acids. 2) An investigation of the effect of electrostatic modifications near the active site of superoxide dismutases on the interaction with O2-/H202 and their dismutation rates and mechanisms. Most of these projects are conveniently studied by the fast kinetic techniques of pulse radiolysis (pr) and stopped-flow (sf) photolysis. In addition, some studies will make use of techniques newly developed in this laboratory involving a combination of sf and pr, that is stopped-flow mixing is implemented either immediately prior to or immediately after pulse irradiation. Irradiated samples will be rapidly quenched to low temperatures for later product analysis. The combined information obtained from kinetic measurements and product analyses will be used to establish reaction mechanisms that will allow a more rational evaluation of similar processes in more complex biological systems.